The proposed research will expand available knowledge about age-related reduction of sleep's intensity that is indicated by lowering of the auditor awakening threshold (AAT) and deterioration of delta (slow wave) activity in the EEG. Major goals are (1) to provide data on the AAT and delta activity more representative of the life span than presently available data (2) to describe the age pattern of changes in the AAT and delta activity, their relationship with each other, and with sleep disturbance, (3) to determine whether reduction of sleep's intensity, as measured by the AAT and/or delta activity, can account for age-related sleep disturbance, and (4) to assess whether the well-known sharp decline in basal metabolic rate over the life span could underlie sleep's deterioration. Data will be collected from 10 males and 10 females at each of the followin age levels: 6 - 10, 13 - 15, 18 - 28, 35 - 45, 55 - 65, and 70 - 80. Computerized analyses of overnight recordings will provide counts of delta waves and measures of the amplitude and duration of delta activity. Whethe changes in AAT and delta activity are linked to sleep disturbance will be determined by assessing their relationship with wakefulness after sleep onset and with arousal during sleep signified by computer-analyzed alpha activity in the EEG. Basal metabolic rate will be measured in each sleeper for assessment of its relationship with all the aforementioned variables. Secondary goals include (1) evaluation of basal skin resistance as a possible measure of age-related change in sleep's intensity, and (2) evaluation of the need for an amplitude criterion for delta activity when comparing the representation of delta activity in visually scored sleep records of young and old.